1. Field of the Invention
The present invention relates to an addressing method and more particularly to a method well adapted for a sector type of magnetic-drum or magnetic-disc memory.
Today, mainly for economic reasons, it is desired to multiply recording densities double or threefold and many attempts have been made for this purpose. However, in case of, for example, threefold multiplication of the recording density, there arises an inconvenience that one band cannot be made up of 2.sup.p sectors (p = positive integer). Hence, there is a need for a completely new method of addressing. Generally, in a system such as a process control computer system wherein real time response has an important significance, it is necessary to freely run a plurality of subprograms or data. Therefore, a sector type device is most preferable in recording in a magnetic-drum memory.
2. Description of the Prior Art
In a conventional data arrangement, k bits (for example, 16 bits + one parity bit) make up one word, l words (for example, 16 words) constitute one sector and m sectors (for example, 64 sectors) complete one band. Each band corresponds to one track on the magnetic drum and the drum contains n bands (for example, 512 bands), that is, n tracks. In this case, the bands are spatially selected while the sectors, words and bits are selected in time sequence. The smallest units into or out of which data are written or read, are sectors and the specification of addresses by the processor is performed according to serial binary codes corresponding to the whole sectors. In the case where the specification of an address is performed with 15 bits in the controller of the magnetic-drum memory device, the lower 6 bits address are set as sector address on a sector register and then selected in time sequence by a sector counter and a coincidence circuit. On the other hand, the upper 9 bits are set on a band register to spatially select a desired track by means of a matrix made up of X- and Y-switches. In the above-described arrangement, one band comprises sectors whose number is equal to 2.sup.p. Therefore, even if one band can be technically allocated by 100 sectors, 36 (= 100 - 64) sectors are left unused as an idle area since the specification of sector addresses by 6 bits enables the addressing of only 2.sup.6 = 64 sectors. In the case where it is desired to utilize 7 bits for the specification of sector addresses, 2.sup.7 = 128 sectors must be provided in one band. Therefore, such an addressing cannot be performed in the case of the allocation of 100 sectors in one band.